Short-circuit transfer gas shielded arc welding, which is a gas shielded consumable electrode arc welding process, includes carbon dioxide gas shield arc welding, mixed gas shield arc welding and argon shielded consumable electrode arc welding, in which a melting drop is deposited from a welding wire or electrode onto a workpiece in a short-circuit transfer mode. Because of it's high productivity, low cost, small welding distortion, popular adaptability, easy to be employed in all-position welding and easy to be automatized, short-circuit transfer gas shield arc welding has wide impact in industry applications. The major disadvantage of short-circuit transfer gas shield arc welding is the huge amount of the welding spatter, which deteriorates the working condition and environment, reduces the welding wire deposit efficiency, affects the arc stabilization and lowers the welding quality.
A typical short-circuit transfer gas shielded arc welding machine comprises a welding power source, a welding wire feeding mechanism and a gas shield system. In the welding process, when the metal drop which is melted from the welding wire is shorted circuit with the workpiece, the short-circuit liquid bridge is formed, and the current in the welding circuit loop is increased consequently. Under the electromagnetic force of the current, the gravity and the surface tension of the melting metal, the liquid bridge shrinks and its diameter becomes smaller and smaller. When the diameter of liquid bridge reaches a critical value, the liquid bridge is broken by the explosion under a very high peak current and the arc state is restored again. In traditional spatter reduction methods, a reactance or electrical reactor is connected in series into the welding power source to restrict the short-circuit current increasing rate, so that the peak current and welding spatter can be restrained. However, to ensure the normal transfer of the melting drop, the shrinkage and transfer of the short-circuit liquid bridge also depend on a very high short-circuit current, and the traditional method still creates significant spatter.
Extensive research was carried out in recent years all around the world. It has been concluded that the spatter is due to the explosion of the short-circuit liquid bridge under the high current during the later period of the short-circuit. Most of the spatter reduction techniques can be classified into the following four categories:                The first category consists in simply changing the gas components, adopting the electrical reactor, or controlling the current increasing rate of the welding circuit loop. By these simple methods, the spatter can be only reduced to a limited degree.        The second category consists in the control of welding wire feeding movement, wherein the liquid bridge is broken by instantaneous drawing back the welding wire, which means the electromagnetic force is substitute by the mechanical force to carry out the melting drop transfer. But the welding wire movement delay in the feeding pipe enables it hardly synchronized with the liquid bridge shrinkage process and the current control process, which makes these methods theoretical but impractical.        The third category consists in the control of the welding current waveform. The process of the melting drop transfer happens randomly, rapidly, and with great diversity. For this reason, the preset current waveform cannot fit each course of the melting drop transfer in real time. Further more, improper waveform control will reduce the arc length self-adjustment property and arc stability, and also affect the penetration, formation and quality of the welding bead.        The fourth category consists in the current control of the power source by monitoring the course of the melting drop transfer. Technically, it is very difficult to detect the state of the short-circuit liquid bridge, so regular detection methods can hardly monitor the course of the shrinkage of the liquid bridge. Some methods detect the voltage, the voltage changing rate and the resistance between the contact tip and the workpiece to describe the diameter of the liquid bridge. But the parameters mentioned above do not represent the exact value of the diameter of the liquid bridge, because all the above detection values include the disturbance and the effect of the liquid bridge current and the resistance of the welding wire extension (the wire length between the contact tip and the top of the liquid bridge).        
Some methods (for example, as disclosed in JP 59-199173) try to use the resistance changing rate between the contact tip and workpiece to represent the state of liquid bridge shrinkage. However, connecting sensor cables to the welding torch and the workpiece is not a practical way in mass production. The sensor cable is easily to be damaged, short-circuited, cut or disabled in on-site environment by the high temperature conditions of the welding arc and the welding workpiece. For most of the semi-automatic welding machine used in industry, it is also very difficult to connect the sensor cable to the contact tip in the welding torch. So, it is widely concerned that how the diameter and shrinkage state of the short-circuit liquid bridge can be accurately measured and detected directly from the output of the welding power source. Concerning the method for the reducing of the liquid bridge current, due to a huge DC reactor inductance is connected in series with the welding power source, which is essential to restrict the output current increasing rate, all the current controls before the DC reactor inductance are ineffective because of the insufficient dynamic response. Due to the DC reactor inductance, none of the controls before the DC reactor inductance can depress the liquid bridge current from about 1000 A to a very low level in about 100 microseconds under the short-circuit condition. The above current control response is much slower than the liquid bridge shrinkage and explosion process. Some other methods attempt to control the later period current of the short-circuit liquid bridge by a power module in series connection in the welding circuit loop. The DC reactor inductance mentioned above would cause an extreme high over voltage on the control module under the fast current changing rate. Contrarily, if the liquid bridge current decreases not so fast, the liquid bridge current cannot be reduced in a short time. Further more, the control module in series connection in the welding circuit loop will cause considerable power dissipation.